The present invention relates to polynucleotide and polypeptides of Human Kv1.3, compositions comprising same and methods of using them.
Ion channels are proteins embedded within the cell membrane that control the selective flux of ions across the membrane, thereby allowing the rapid movement of ions during electrical signaling processes. Because ion concentrations are directly involved in the electrical activity of excitable cells (e.g., neurons), the functioning (or malfunctioning) of ion channels can substantially control the electrical properties and behavior of such cells. Indeed, a variety of disorders, broadly termed as “channelopathies,” are believed to be linked to ion channel insufficiencies or dysfunctions.
Ion channels are referred to as “gated” if they can be opened or closed. The basic types of gated ion channels include a) ligand-gated channels, b) mechanically gated channels and c) voltage-gated channels. In particular, voltage-gated channels are found in neurons and muscle cells. Voltage-gated ion channels open or close in response to changes in the potential differences across the plasma membrane.
Voltage-gated and ligand gated ion channels have been mapped in various excitable tissues including secretory tissues (e.g., kidney, liver, pancreas), the heart and the neural tissues (e.g., autonomic neurons). Medications that are directed to ion channels account for a major pharmaceutical market segment. Such drugs increase or decrease the flux of ions through those ion channels to bring about desired therapeutic effects.
Modification of the excitability of cardiac tissues by overexpression of specific ion channels have been previously described (Hoppe U C, Marban E, and Johns D C. Molecular dissection of cardiac repolarization by in vivo Kv4.3 gene transfer. J Clin Invest 105: 1077-1084, 2000). Briefly, overexpression of the KV1.3 gene was shown to significantly shorten the action potential duration in myocytes having a normal action potential duration at baseline.
Alternatively, transplantation of cells overexpressing ion channels was also suggested for excitable tissue modulation (Yair Feld, Meira Melamed-Frank, Izhak Kehat, Dror Tal, Shimon Marom, Lior Gepstein. Electrophysiological Modulation of Cardiomyocytic Tissue by Transfected Fibroblasts Expressing Potassium Channels: A Novel Strategy to Manipulate Excitability. Circulation. 2002 January; 105: 522-529; see PCT Publication No. WO2006/018836).
Prolongation of the refractory period is one strategy for the treatment of cardiac arrhythmias. The voltage gated Kv1.3 channel expresses a long tail current causing it to be attractive as a potential modulator of the cardiac effective refractory period (ERP) when overexpressed by cardiomyocytes or other cells electrically coupled with cardiomyocytes. It was previously demonstrated that rat Kv1.3 channel in which the histidine at position 401 was replaced by tryptophan (Kv1.3 H401 W) introduced a rapid inactivation property to the channel (Kupper J, Bowlby R M, Marom S, Levitan BT. Intracellular and extracellular amino acids that influence C-type inactivation and its modulation in a voltage-dependent potassium channel. Eur J. Physiol. 1995; 430: 1-11). Preliminary analysis suggested that the effect of the mutation is caused by slowing down of the recovery rate from inactivation. In this channel recovery from inactivation involved passing through the open state. It was demonstrated that the mutant channel has significantly long tail current (American Society of Gene Therapy 8th Annual Meeting. Refractory Period Prolongation by Fibroblasts Overexpressing the Mutant Kv1.3H401W Channel in Computer Simulation and Pig Hearts. Shabtay A, Bresler T, Yankelson L, Gepstein L, Marom S, and Feld Y. 2005.). Shabtay et al also demonstrated stronger effect in prolonging of the refractory period of pig hearts at specific loci by transplantation of fibroblasts overexpressing the rat Kv1.3H401W vs. the wild type Kv1.3 channel by computer simulation and in vivo experiments.
Interestingly, reported mutations in the S6 domain of human Kv1.3 (H399T and optionally A413C) were shown to mediate an opposite effect to that of the 11401 W, essentially reduction in the C-type inactivation of the channel and faster recovery rate.
In another report A413V mutation of hKv1.3 was shown to actually increase inactivation of the channel, however use of same for the treatment of various pathophysiologies has never been suggested [Panyi (1995) Biophysical Journal 69: 896-903].
There is thus a widely recognized need for and it would be highly advantageous to have hKv1.3 mutants with increased C-type inactivation rate and methods of using same in human therapy and drug screening.